1. Field of the Invention
This invention relates primarily to fabrication of group IIIA-VA semiconductor materials and also to zinc blende semiconductors, diamonds and the like and, more specifically, to improving the mechanical properties, primarily of group IIIA-VA semiconductor materials, but not limited thereto.
2. Background and Brief Description of the Prior Art
Group IIIA-VA compound semiconductor materials and particularly gallium arsenide (GaAs), gallium phosphide (GaP) and indium phosphide (InP) are becoming important optical materials for use in the infrared (IR) and microwave regions of the electromagnetic spectrum. These uses include windows, domes, lenses, etc. for use in electro-optical systems such as forward looking infrared (FLIR) systems, IR warning and target systems and seeker systems. In many of these applications, use of GaAs is very limited or the GaAs is not used at all because of its relatively poor mechanical properties.
Single crystal and large (&gt;1 mm) polycrystalline GaAs and other single crystal and polycrystalline group IIIA-VA semiconductor compounds are generally brittle, possessing cleavage planes along which they can very easily crack apart. While the cubic zinc-blende crystallographic structure of GaAs results in many such cleavage planes, the predominant cleavage plane is the {110} family of planes because they require the least amount of stress to crack or cleave them apart. These cleavage planes represent a path along which a crack can propagate by a driving force of very low stress. Because all optical quality GaAs is produced as either single crystal or large polycrystalline material, the cleavage planes will traverse or nearly traverse the physical dimensions of whatever optical sample is fabricated. Due to the low stress levels required to separate them and the degree to which they extend through the sample, the cleavage planes seriously reduce the fracture strength of the GaAs optical components.
The low fracture strength of GaAs wafers for digital and microwave electronic devices results from the same problem of cleavage planes. The problem in optical quality GaAs as opposed to semiconductor quality GaAs is emphasized herein only because it is much more limiting to the potential uses of the material for that purpose.
In most crystallographic planes, the intrinsic bond strength of GaAs is very high. If these strengths could be maintained throughout the entire GaAs component, the fracture strength would be sufficiently great to permit the use of optical quality GaAs in such applications as high speed windows and domes on aircraft and missiles or any other application, optical or electrical, where high mechanical strength GaAs would be desired. This toughening process also has a significant effect on the yield of GaAs-based electronic devices, such as digital or microwave circuits, by reducing the number of GaAs wafers lost in the front-end fabrication due to cracking, thereby providing a significant economic advantage.
To date, there is no known literature relating to attempts to strengthen GaAs, primarily relating to its fracture strength.